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Hi John,
That sounds a bit odd. Can I check that the spectrum definitely calibrates successfully. If you hover the mouse over the spectrum plot in tab 5, then do you see sensible wavelength numbers appear for the cursor position in the bottom left of the screen?
Also, you say you are not using the Alpy calibration module. Are you using an A type star, or similar star with prominent hydrogen lines to wavelength calibrate your spectrum? Or are you using a neon lamp source, just not the one that comes with the ALPY, in which case you may be able to select the “ALPY 600 (with calibration module)”.
Cheers,
Andy
The software is in testing and it has not been officially announced. So I’m not sure if it should be discussed publicly on the BAA forum. I’ve emailed the developer to check.
Andy
I did once have condensation forming on my CCD coverslip. This can happen with some CCDs when they are kept in a damp environment.
I now place a silicon desiccant bag in my telescope tube when I’m not using it, which I replace and reactivate every so often. I’ve not had any problems since doing this.
Andy
Hi Kate,
It is one of the idiosyncrasies of ISIS calibration for the Alpy that you have to tweak the value of the pixel size. This goes against common sense as of course the pixel size is fixed.
I think this is because no 2 Alpys are quite identical, and is due to minor differences in focal lengths and chip to grism distances. François Cochard explained this at the BAA workshop far better than I can remember it now, but I remember that tweaking the pixel size fixes the problem.
Best wishes,
Andy
Hi Steve,
A couple of interesting spectra.
With regard to choice of star for the response, as well as choosing an A or B type star the other factor is to have a good professional spectrum to produce the response curve. Stars from the MILES database are the common choice, as this has good coverage across the sky. In a previous post Robin gave a link to a very useful spreadsheet developed by Paolo Berardi which allows you to search for MILES A or B stars for coordinates of interest.
https://britastro.org/node/8152
I think Castor is a reasonable choice, though Robin and David have more experience in choice of good stars for low resolution spectroscopy than I do. Though it is a double star which might make me think twice about using it, it is in the MILES database (HD060179), so that means there should be a good professional reference spectrum.
Cheers,
Andy
Hi Nick,
I have an 55W electric tube heater which I leave on in my observatory. I also have a cold air dehumidifier which I run for a couple of hours after I’ve closed up my observatory. I find things due up during an observing session, and this takes away the moisture. This is particularly important for me as I leave a desktop computer in my observatory.
Andy
Hi Bill,
That is a fantastic looking spectrum with lots of features in it.
If you are able to convert your meteor spectra to 1D FITS format then you will be able to load them into the new BAA Spectroscopy Database. Let me know if you are interested and if I can be of any assistance.
Cheers,
Andy
Very interesting. There is also the SPHERE instrument which is mounted on the VLT.
http://www.eso.org/public/unitedkingdom/teles-instr/vlt/vlt-instr/sphere/
Hi Steve,
I’m not really an Alpy expert but I do agree that looks a bit odd. Was it taken in darkness or daylight? Just in case stray light might have been getting in. Also, do you know if that bright “line” is oversaturated and do you have an approximate idea of its wavelength from your wavelength calibration.
Best wishes,
Andy
Hi Tony,
The new BAA Spectroscopy Database could well be the ideal place to share and compare results, assuming people have reached the stage of producing 1D fits files from ISIS.
I’m just looking at making a final tweak before go-live. This would be to add a “flat field” flag. Though in theory all spectra should be flat fielded before submission, there may be cases where this is not possible, hence why we might want to record that information.
I’ve been busy since the workshop, so I’ve not had a chance to work on this change. If I can’t find the time to do it within the next few days then we’ll probably go-live without it to avoid further delay.
Best wishes,
Andy
I think I suffered from the chromatic aberrations for a time. It looked as though I had a problem with the slit drifting across the star image, so sampling different parts of the image that had been colour dispersed by the Earth’s atmosphere.
Here is a plot that shows the result as the continuum varies, just looking at 2 points in a series taken 20 minutes apart. I’m glad to say I’ve not suffered from this problem recently.
Andy
That is a decent guide image Tony. I find that for good results the target star has to be bang on the slit. This is not just to get the maximum number of photons through the slit, but also to avoid sampling parts of the star’s image which may have been colour dispersed by the atmosphere.
Cheers,
Andy
Hi David,
I have a Starlight Xpress SXVR-H694 and I usually run it at -20C. During the Winter months I sometimes run it at -25C. Of course I have to make sure I have a full set of darks and flats to match whichever temperature I use.
I agree with what Francois said, it is important to run your camera at a temperature that it can easily maintain, so that you do not get too much temperature drift. I find the temperature drifts by a few 10ths of a degree, but no more during my exposures.
Best wishes,
Andy
Hi Steve,
I’d also like to thank David and Ann for organising such a great weekend, and to Francois Cochard for all the work he put into the presentations and demonstrations. Thanks for your kind words on the database. Watch out for an announcement sometime soon..
I would also like to re-emphasize to everyone who attended the weekend, and to all BAA members, the forum is a great place to ask questions and share results, even if your results don’t look right. Starting out in spectroscopy is hard. One of the tools that makes this possible today is the internet. It is quick and easy to share results and ask questions. Remember there is no such thing as a stupid question. There are probably others out there struggling with the same problem as you.
If anyone from the weekend has trouble accessing the forum then drop me an email.
Best wishes,
Andy
Hi Tony,
Thanks for the file. I’ll be at the spectroscopy workshop, so hopefully there will be a chance to discuss photometry file formats.
I’m unlikely to have the time to work on this until next year. I’m studying at weekends and have several meetings to attend in the run up to Christmas. Once my schedule has calmed down, then that will be the ideal time to look at the format in more detail and make the changes. Having sample files to work with will be a big help, as I’m not currently setup to do my own photometry.
Cheers,
Andy
Hi Graham,
You could also try emailing William-Bell to see if you can get hold of the book and software, or maybe just the software if they have run out of the books.
http://willbell.com/contact.htm
The other thing to watch out for is if you find a copy to make sure it is version 2. William-Bell used to offer an upgrade from v1 to v2, but I’m not sure if that is still available.
Andy
Hi Tony,
AIP4Win MMT does not produce files in the BAA VSS format. It is on my list of things to do to amend the VSS Photometry spreadsheet to read the MMT files, but that is likely to be at least a few months away. (Anyone could create a spreadsheet or other application to do the conversion but I suspect it will wait be me to produce something.)
Another one of the items on my to do list is to investigate building compatibility in to the VSS Database website for loading the AAVSO data format. The main issue here is the last time I reviewed the AAVSO format it did not provide all of the data we store in the BAA VSS database. However, we may just accept that we do not get all of the data.
I’ve not had a chance to look at the MMT format recently, so perhaps you could email me a copy? That will give me an idea of how much work the development will be.
Thanks,
Andy Wilson (BAA VSS Database Secretary)
Congratulations Robin. A great achievement to take the confirmation spectrum for a mag 16 supernova!
Cheers
Andy
That is a fabulous spectrum for such a faint target Robin. A shame you were clouded out but this is another demonstration of what you can achieve with your setup.
Andy
I very much hope that a digital subscription will be rolled out as an option to all members in the near future. I would like to take advantage of this cost efficient way of being a member, with the ability to access to the journal and handbook online. I subscribe to a number of astronomical organisations and magazines and the annual total is not insignificant. So I applaud initiatives like this.
Andy
